When your best intentions go south, new research suggests that it wasn’t the devil that made you do it. It was your brain.

Will power, the study found, is a finite resource, one that can be easily depleted. Which is why, when faced with a “do-I-or-don’t-I” kind of decision, you might find it easier to do the right thing when you haven’t already used up your reserve of self-control by forgoing that extra cocktail earlier in the night.

Oddly reassuring, right?

The study, to be published January 2013 in the Journal of Consumer Psychology, suggests that self-control is not a muscle that grows stronger with exercise, but is more like a finite pool. And when it gets drained, say, by saying no to that delightful little black dress you just tried on but don’t necessarily need, you’re more likely to lose your cool when that guy in the silver SUV cuts you off on the freeway driving home.

Or, for that matter, to have that second glass of Malbec once you get there.

The study, co-authored by William Hedgcock, assistant professor of marketing at the Tippie College of Business at the University of Iowa, used brain imaging to scan people as they performed self-control tasks. The fMRIs found that the brain consistently fired at full speed when tasked with recognizing a temptation, but once the part of the brain that actually manages self-control took over, it fired with less intensity the longer it continued to fight the good fight.

“Our results suggest self-control can be diminished by use,” Hedgcock tells us. “People have a hard time resisting temptation after prior acts of self-control. This can negatively affect people’s ability to maintain attention, resist tempting snacks, and resist purchasing on impulse.”

Call it good-girl fatigue? Your brain may have no trouble recognizing the naughty options, but the more you try to fight them, the harder it can be to do what’s right. Or why, as the authors write, when we work hard to pass up a second helping of lasagna, we might end up taking two pieces of cake at dessert. And while the study found no significant gender differences, writes the study’s co-author Kathleen Vohs, associate professor of marketing at the University of Minnesota, in an email from Amsterdam, “men and women often do adopt different goals (e.g., to lose weight for women [or to] pursue financial or sexual rewards for men) but they do so in similar ways.”

What’s hugely important about the study, writes Vohs, is that “we haven’t had a good understanding of how the brain changes when people engage in self-control. Which means being able to ultimately understand self-control in new ways.”

For years, researchers have known that there’s some significant work going on upstairs when we try to make decisions (whether or not those choices involve resisting temptation) about anything from buying a new pair of jeans to figuring out what to do with our lives. Many studies we’ve referenced in our book and our blog, in fact, have shown that any kind of mental overload can mess with our ability to make good choices — or any at all. A pivotal study by Harvard psychologist George Miller back in the 1950s found that the rational brain can only hold about seven chunks of information in working memory at any given time. Any more, and the conscious brain often just throws up its hands in defeat. What psychologists have figured out since, is that when the cognitive brain gets too full, decision making—if it gets done at all—gets appropriated by the emotions. Because the rational brain has, in effect, logged off, there’s less control over gut impulses.

Some fifty years after Miller’s essay, Stanford marketing professor Baba Shiv put an interesting spin on this epic battle between heart and mind. In his study, he asked students to memorize either seven digits or two, then afterward offered both groups their choice of a reward: fruit salad or gooey chocolate cake. What he found was that the seven-digit group went with their gut instincts. They overwhelmingly chose cake. The two-digit folks? They made the rational decision and chose a snack that wouldn’t spoil their dinner: nice and healthful fruit salad.

A number of other studies have also shown that making choices just plain wears us out, which brings us back to some earlier work on self-control by Kathleen Vohs. Back in 2008, she found that folks who are faced with too many choices have a tough time staying focused or exerting self-control afterward. In one part of that study, she found that college students asked to make a number of random choices earlier in the day ended up spending more time later playing video games or reading magazines — rather than studying for a test.

But back to this particular study, Hedgcock suggests that when the well of self-control runs dry, the only way to fill it back up is with time. In other words, give yourself a break.

Thanks for the offer. But let’s just have some chocolate cake and call it a day.

More about this cake business later, but first, there’s this: Newsweek is the latest to hop aboard the streetcar named Can’t Decide — our own trek for the past two years — with its current cover story on the “twitterization” of our culture, or why we can’t think.

The story references research by Angelika Dimoka, director of the Center for Neural Decision Making at Temple University, who found that information overload mucks with our ability to make decisions — and control our emotions:

“With too much information, ” says Dimoka, “people’s decisions make less and less sense.”

So much for the ideal of making well-informed decisions. For earlier generations, that meant simply the due diligence of looking things up in a reference book. Today, with Twitter and Facebook and countless apps fed into our smart phones, the flow of facts and opinion never stops. That can be a good thing, as when information empowers workers and consumers, not to mention whistle-blowers and revolutionaries. You can find out a used car’s accident history, a doctor’s malpractice record, a restaurant’s health-inspection results. Yet research like Dimoka’s is showing that a surfeit of information is changing the way we think, not always for the better. Maybe you consulted scores of travel websites to pick a vacation spot—only to be so overwhelmed with information that you opted for a staycation. Maybe you were this close to choosing a college, when suddenly older friends swamped your inbox with all the reasons to go somewhere else—which made you completely forget why you’d chosen the other school. Maybe you had the Date From Hell after being so inundated with information on “matches” that you chose at random. If so, then you are a victim of info-paralysis.

We devoted a whole chapter in our book to the science of decision making (and several posts, like this one, from over a year ago) Like Newsweek, we found that too many options sends the brain into overdrive, at which point it often says screw it and just goes off to bed. Also like Newsweek, we found that the constant beep and buzz of the electronica that has become a part of our every waking moment just adds to the chaos, making it close to impossible for us to make a decision — or be happy with it when we do.

A lot revolves around a pivotal 1950’s study, cleverly titled “Magical Number Seven, Plus or Minus Two”, that found that your rational brain can only hold about seven different things in working memory at any one time. More than that, and your head starts spinning. Ms. Rational Brain is likely to say “I quit” — and cede control to the emotional brain.

If you’re thinking this can’t end well, you’d be right. This is where the chocolate cake comes in.

Several decades after that pivotal study, a Stanford marketing professor named Baba Shiv tested the theory with a bunch of hungry college students. He had one group memorize two-digits — and the other group, seven. Afterward, they were offered their choice of reward — fruit salad or gooey chocolate cake — and guess what happened? The crew that was overloaded with info overwhelmingly chose cake. The two-digit folks? Fruit salad, please.

You can guess which group might have had some regrets a little later. Which brings us to our point. When you are overloaded with information — or options — decision making becomes a labyrinth of twists and turns that rarely has a happy ending. We second-guess. We regret. We start jonesing for the greener grass. Add the constant distractions of Facebook, Twitter, smartphones and [insert Next Big Thing here] and it’s no wonder we can’t decide what to have for dinner, much less what to do with our lives.

All of which is that much worse for women when it comes to what-do-I-do-now decisions. Why? Generational, sister. Suddenly we’re faced with more options than our mothers or grandmothers ever thought possible, and we’re running the road without a map. Or role models, either. We can be doctors. We can be lawyers. We can run off to join the circus. We can stay home to raise kids. We can stay home to write books. We can do anything. We can do everything. So how do we choose? Especially when, as Shannon wrote on Tuesday, we live on a steady diet of news feeds, tweets and other app-philia from the land of perfect, all of which seem to proclaim: Look at me! I’ve gotten it right. Ahem, and you?

And me? Sigh. There’s more about the science of decision making in the Newsweek piece, and lots more than that in Chapter 5 of our book. And in fact, I could add quite a bit more to this post. But you know what? There’s chocolate cake in the office down the hall, and I’m headed that way. And you don’t have to tell me: You want some too.

There is a point here, I promise. But first, here’s the scene. My desk, at work. A wobbly stack of books, papers and files, some dating back to last spring. A to-do list, also written last spring. On the other side of my mousepad, a pile of resumes for the letters of rec I need to write. On my computer, some 200 emails that at least have to be opened.

Plus the steady buzz of folks, either in the hall, or in my office. Kinda like a roving cocktail party, but without the booze. This is not necessarily a good thing. The latter, I mean.

My home office, not much better. At least 100 unread emails. My desk is cleaner — today — but you still never know what you’ll find. A friend once described my work-at-home digs as a junk drawer. At times, the description is apt.

On Tuesday I got up early, graded papers, scanned two newspapers, got ready for school, found and paid my Macy’s bill while my Cheerios got soggy, blew out the door and off to work, taught some classes, and met with a bunch of students who have the end-of-quarter heebie-jeebies. (They’re contagious).

Last week, we hosted a party to celebrate a friend’s engagement. Next week is Thanksgiving (Yikes! I forgot to order the turkey). It’s my husband’s and son-in-law’s birthdays. Shannon and I are knee-deep in writing this book. And this blog. My hair is stringy and I’m low on clean clothes. So here I am.

Don’t get me wrong. I fully realize that those balls I’ve got in the air mark me as a lucky woman. Nonetheless, I’m somewhat breathless just itemizing all this. I’m frazzled. Distracted. And probably like you, just a little bit crazed: Too much going on, going on all at once.

Maybe it was ever so. But now, add this. The San Francisco Chronicle has reported on some new studies on the way that techno-stimulation — texts, tweets, IMs, Facebook, news alerts, the list goes on — has led to a new form of attention deficit disorder. We’re always on. Uber-connected. Addicted to short bursts of constant information. And despite our best intentions, we get sucked in. All of which, experts say, impacts our ability to analyze. From the story:

“The more we become used to just sound bites and tweets,” [Dr. Elias Aboujaoude, director of Stanford University’s Impulse Control Disorders Clinic at Stanford University] said, “the less patient we will be with more complex, more meaningful information. And I do think we might lose the ability to analyze things with any depth and nuance. Like any skill, if you don’t use it, you lose it.”

Dr. John Ratey, an associate clinical professor of psychiatry at Harvard Medical School, uses the term “acquired attention deficit disorder” to describe the way technology is rewiring the modern brain.

I don’t know about you, but I really don’t need to know what Suzy from Ohio is doing every five minutes. And yet. There’s the seduction of the buzz, the flash. She has me at beep-beep.

Which brings me belatedly to my point: Is all this stuff, this stimulation, this juggling, cluttering up our already cluttered brains to the point where we are not only overwhelmed — but chronically undecided?

The science suggests the answer is yes. Shannon wrote earlier on our blog about the Paradox of Choice, about how the more choices that confront us, the less likely we are to make one — or to be happy with it when we do. There’s the iconic jam study, where shoppers confronted with 24 jars of jam — versus just six — walked away empty handed. And the pivotal Magical Number Seven study, which dates back to the 1950s, that found that the human brain has trouble processing more than seven items at a time. The study was the basis for similar research in 1999 by Stanford Marketing Professor Baba Shiv, then an assistant professor at University of Iowa. He sent two groups off to memorize a series of numbers. One group had to memorize three. The other, seven. At the end of the task, the groups were given their choice of a treat: gooey chocolate cake or fruit salad. The three digit group overwhelmingly chose fruit. The seven digit group — cake. The point? Overwhelmed with the memory task, the rational brain of the seven-digit folks begged off and let the emotional side take over.

Shannon wrote recently about Zen and art of multi-tasking where, really, what we need to do when we drink tea –is to just drink tea. I wrote about the need to just play cards. Put all of this together and I think you find that maybe, for our own mental health, not to mention our ability to make decisions, we need to turn down the chatter.